Fixing prints of stabilized azoic and reactive dyes on cellulose and cellulose/polyester

ABSTRACT

A process for printing and continuous fixation of stabilized dyeing preparations forming azo dyestuffs and of reactive dyestuffs on textile materials containing cellulose or consisting exclusively of cellulose material, comprising a continuous working process of steaming the material printed with the dyeing preparations and reactive dyestuffs, for a short time for developing and fixing the azo dyestuffs using high concentrations of volatile acids with or without use of a counter-current operation method, and of treating then the material according to a known two-phase-fixation process for fixing the reactive dyestuffs and finishing it as usual by washing, soaping and rinsing as well as a process comprising the said very rapid fixation process of stabilized dyeing preparations forming azo dystuffs, by means of acid steam except for the use of reactive dyestuffs and for the use of the two-phase-fixation process which leads to dyeings of azo dyestuffs and of reactive dyestuffs of good fastenesses and brilliancy obtained in a very short time by means of a fully continuous process of fixing azo and reactive dyestuffs and of after-treatment the dyed material.

United States Patent [1 1 Feess et al.

[ Mar.5, I974 FIXING PRINTS 0F STABILIZED AZOIC AND REACTIVE DYES ON CELLULOSE AND CELLULOSE/POLYESTER [75] Inventors: Erich Feess, Lorsbach/Taunus;

Willy Gronen, Hofheim/Taunus, both of Germany [73] Assignee: Farbwerke Hoechst Aktiengesellschaft vormals Meiter Lucius & Bruning, Frankfurt/ Main, Germany [22] Filed: Oct. 13, 1971 [21] Appl; No.: 189,043

[30] Foreign Application Priority Data Oct. 15, 1970 Germany 2050631 [52] US. Cl. 8/21 C, 8/26, 8/1492,

[51] Int. Cl .I D06p 3/82 [58] Field of Search 8/21, 26, 149.2, 149.3

[56] References Cited UNITED STATES PATENTS 3/1971 von der Eltz et a1. 8/21 C OTHER PUBLICATIONS Fortess et a1., ADR, 5/27/63, p. 16-25. Wygand, ADR, 12/7/64, p. 106109.

Primary Examiner-George F. Lesmes Assistant Examiner-Patricia C. Ives Attorney, Agent, or FirmCurtis, Morris & Safford [57] ABSTRACT I material according to a known two-phase-fixation process for fixing the reactive dyestuffs and finishing it as usual by washing, soaping and rinsing as well as'a process comprising the said very rapid fixation process of stabilized dyeing preparations forming azo dystuffs, by means of acid steam except for the use of reactive dyestuffs and for the use of the two-phase-fixation process which leads to dyeings of azo dyestuffs and of reactive dyestuffs of good fastenesses and brilliancy obtained in a very short time by means of a fully continuous process of fixing azo and reactive dyestuffs and of after-treatment the dyed material.

8 Claims, No Drawings FIXING PRINTS OF STABHLIZED AZOHC AND REACTTVE DYES N CElLLULOSlE AND CELLULOSE/POLYESTER The present invention relates to a process for printing and continuous fixation of stabilized dyeing preparations forming azo dyestuffs, and of reactive dyestuffs on textile materials containing cellulose or consisting exclusively of cellulose material.

lt is known that by applying diazotized amines besides or in mixture with reactive dyestuffs on cotton fabrics, which have been previously impregnated with alkaline solutions of B-oxynaphthoic acid arylides, prints may be obtained which represent an optimum as concerns low price and brilliance. This operation method implies as a further advantage the continuous fixation of the dyestuffs on the fibre. The diazotized amines are coupled directly with the naphthol derivative on the fibre to form the final dyestuff, whereas the reactive dyestuffs are fixed by afive second-diving process in a hot alkaline solution, which contains very large amounts of salt. This method is especially recommended, if at least 30 percent of the naphthol bottom is utilized by coupling with the diazonium salts for achieving a toning.

However, the different steps of this method (applying the naphthol derivative before the printing process itself) are inconvenient. Moreover, one and the same naphthol derivative applied onto the fabric by padding and used as bottom is only suitable for achieving a certain and limited number of shades.

This disadvantage has already been overcome previously by the development of stabilized dyeing preparations, which contain as substantial constituent a naphthol derivative and stabilized diazo compounds; by printing the fabric with different types of this dyeing preparations, various shades may be produced on the fibre, which permits independence from the respective bottom. The mentioned stabilized diazo compounds are for example diazo-amino compounds obtained by reacting the non-stable diazonium salts with for example cyanamide, anthranilic acid or other amines. They are sufficiently stable in the alkaline medium for being combined with naphtholate solutions. It is also possible to convert the diazotized amines into anti-diazotate compounds with the aid of strong alkalis, and their mixtures with naphtholates lead to similar, however less stable dyeing preparations.

Dyeing preparations of the mentioned type are in commerce since many years; their stabilized diazo compounds may be converted again on the fibre into the diazotized base by steaming processes, in which case coupling takes place with the coupling component, preferably with a naphthol'derivative, to form the dyestuff. If steaming is effecting in an acidic medium, more brilliant shades are obtained than in the case of neutral steaming. Depending on the steaming devices used, recommendations found in literature are for steaming processes of 35 or of 5-7 minutes. However, these steaming periods are so long that a continuous working, for example continuous steaming and washing may hardly be realized in practice if the best possible speeds of the. washing process shall be achieved. The long steaming periods are due to the fact that in the case of the usual steamers of rather big volume, the content of acid of the steaming atmosphere decreases in close vicinity to the fabric printed with an alkaline agent and that the fabric has not sufficient amount of acid available for developing the diazonium salts and the azo dyestuffs.

Furthermore, the steaming periods are too long to permit reactive dyestuffs, applied on the fibre simultaneously with the dyeing preparations or by overprinting to be fixed subsequently to this steaming process in a continuous two-phase-fast-fixing process.

It has now been found that the reverse transformation of the stabilized diazotized amine on the fibre during the steaming process into the diazonium salt capable of coupling, and the coupling with a coupling component, for example with derivatives of naphthols, B-oxynaphthoic acid amides, with hydroxy-carboxylic acid amide derivatives of the carbazole, of the ben-' zocarbazol, of the anthracene, the diphenyl, the thia- 201, the benz'othiazol, the carbazothiazol, the diphenylene oxide and of other substances, and the fixation of the resulting azo dyestuffs may be realized in a few seconds, if the acid-containing steam is forced to penetrate into the fabric more rapidly and more completely with the aid of the steaming apparatuses described below. This method according to the invention also permits to utilize the acid in the best possible way, whereas in the commonly used steaming devices, large portion of the acid escapes with the exhaust steam from the steamer without being completely utilized. in the case of the steaming devices according to the invention having suitable mechanical conditions for this process, a 5 second-steaming period if thin fabrics are treated, a shorter steaming time is sufficient to ensure a complete splitting of the stable diazo compound and fully developing of the azo dyestuff. The steaming aggregates used for these short steaming processes are therefore very small, so that devices of this kind may be intercalated without difficulty into the continuous development of a production process.

Thus, the present invention relates to a process for printing and continuous fixation of stabilized dyeing preparations forming azo dyestuffs, and of reactive dyestuffs on textile material containing cellulose or consisting exclusively of cellulose material. This process is characterized by the fact that thematerial printed with the dyeing preparations and reactive dyestuffs is steamed for a short time in a continuous working process for developing and fixing the azo dyestuffs by means of high acid concentrations and, if desired, of a counter-current operation method, and that the material is treated thereafter according to a known two-phase-fixation-process for fixing the reactive dyestuffs and finished as usual by washing, soaping and rinsing.

For developing above-mentioned dyeing preparations forming azo dyestuffs according to the process of the invention, there are used steaming aggregates which ensure a necessary intense admission of the acid vapor to the fabric and/or a high concentration of acid on the fabric.

The processes for fixing the dyestuffs of both types had to be carried out hitherto at very different transport speeds and fixation times; according to the present process, the development and fixation of both types of dyestuff may be effected at the same transport speed and therefore in a short time and as continuous working process. If the production yield of the acid-steaming according to processes hitherto known should be assimilated to the yield of a two-phase-fixation process 3 for reactive dyestuffs, up to 60 times the volume of the acid steamer with the number of rollers increasing accordingly would be necessary; thus, due to the necessary resistance to acids of the steaming material, very expensive apparatuses would be required.

As steaming devices transformed according to the invention for the short-time steaming and suitable for this purpose, there may be mentioned:

Channel steamers having a very narrow channel and, if desired, additional obstacles for the vapor, in which the vapor flowing in is enriched with acid by spraying volatile organic acid by means of a inlet pipe or by introducing these acids dropwise onto a heated plate directly behind the vapor inlet pipe, in which process this acid vapor is guided towards the fabric which passes through the steamer (counten r current principle);

Rapid steamer System Hoechst, a channel steamer manufactured in a folded form, provided, if desired, with obstacles for the vapor, in which the vapor is enriched with acid, as indicated above, and guided towards the printed good.

Large-size steaming chambers, for example of the Mather-Platt type, in which the good is passed over rollers arranged at the top and at the bottom and in which, by installing closely arranged partitions between which the textile material is passed and which are alternatively fixed at the top and at the bottom of the steamer, a long folded narrow channel is formed, containing, if desired, additional obstacles for the vapor, and in which the vapor enriched with acid is guided towards the printed good, as described above. By these measures a considerably improved productivity is achieved.

A device particulary suitable for the process of the present invention is the so-called perforated drum steamer according to Belgian Patent specification No. 741,831, in which the printed fabric is led around a perforated drum, through which the vapor enriched with acid is suctioned into the drum, passing through the fabric.

I The acid may also be contacted with the acid completely or in part by printing preferably the non-printed side of the good with relatively concentrated acids using a-so-called thousand point roller (finely engraved roller). A relatively uneven application of the acid in this process practically implies no danger for the quality of the print, since the acid is levelled at any rate by the vapor in the steamer. However, it is also important in this case that a close contact of the vapor atmosphere with the good is ensured or that the vapor atmosphere having reduced its content of acid is immediately replaced by an acid-containing atmosphere by guiding the vapor through the textile material, as in the case of the perforated drum steamer or partly with the aid of obstacles, or by a closely constructed channel. The counter-current method has the further advantage that the acid used is economically better utilized. in the case of the perforated drum steamer the acid is utilized to an optimum by making the vapor circulating and new amounts of acid which is used up by neutralization of the alkalis contained in the print and by absorption by the fabric are continuously added to the circulating vapor.

As acids there are commonly used volatile organic acids, in general acetic acid or formic acid or mixtures of both acids.

I group,

For example the use of a folded channel steamer, for example the rapid steamer System Hoechst having a transport speed of 6m, permits to obtain according to the previously described method at a 5 secondsteaming time, a development and fixation speed of 72m/min., which corresponds absolutely to the speed of a usual two phase-steaming device for fixing reactive dyestuffs; thus, both devices may be combined, in which process both types of dyestuff may be developed and fixed continuously. Thus, it is taken advantage of v the low cost of the stabilized dyeing preparations forming azo dyestuffs, without complicating the operation method.

Such an overall device suitable for the continuous fixation of reactive dyestuffs besides and in overprints with stabilized dyeing preparations forming azo dye stuffs, may also consist of a rapid steamer and a wet fixing box, the latter having also a transport speed of 6m; thus, in both fixing apparatuses the fixation time amounts to 5 seconds. The investment volume for both plants is much smaller than the volume of one individual acid steamer of traditional structure, which represents also a technical progress.

As concerns the behaviour of the reactive dyestuffs, however, the operation method depends on two criteria: During the short time of acidsteamin g, the reactive dyestuffs must not be submitted to acidic hydrolysis and furthermore, it must be possible to fix them on the fibre by an equally short fixation process. Suitable dyestuffs are preferably reactive dyestuffs reacting to an ether bond with the hydroxyl group of the cellulose and belonging to the type of the ,B-oxyethylsulfone-sulfuric acid ester and -phosphoric acid ester as well as reactive dyestuffs possessing one or several N-methyl'N-B- sulfatoethylsulfonamido groups, B-sulfatoethylaminosulfone groups, chloropropionylamido groups, B-sulfatoethylcarbonamido groups, phenylpropionylamido sulfone groups or 2,2,3,3tetrafluorocyclobutane-l-acryloylamino groups. Under certain precautions, by which the sensitivity to the acidic hydrolisis may be reduced, for example by adding sodium acetate to the printing paste, there may also be used in the present process quite a'series of reactive dyestuffs reacting to an ether bond-with the cellulose, for instance dyestuffs containing a monoor dichlorotriazine a -trichloropyrimidine group, a dichloroquinoxaline, or dichloro-phthalazine group, or the like.

medium. The fixation temperature of the acid-steaming must at least amount to C'in this case.

However, the simultaneous fixing of the disperse dyestuffs during the acid-steaming of the dyeing preparations forming azo dyestuffs may be effected more rapidly, if acid-steaming is not carried out in an aqueous vapor medium but in a solvent vapor, for example ethylene glycol vapor. In this case, steaming times of 5 to 10 seconds at temperatures of from to 200C are sufficient. However,. if solvents containing hydroxyl groups are used in the steaming process, these ones have to be eliminated by an intermediate drying process before wet fixing, since the fixation of the reactive dyestuff is affected adversely as concerns its yield.

The following Examples serve to illustrate the invention. The Colour lndex numbers were taken from the 2nd edition 1956 and the supplementary volume 1963 of Colour Index.

EXAMPLE 1 15 g of a commercial dyeing preparation from the coupling component of the Colour Index No. 37505 and the stabilized diazonium compound having the Colour Index No. 37 175 were dissolved cold under addition of 20 g of a 32.5 sodium hydroxide solution 50 g of ethanol 200 g of water and 50 g of urea, introduced while stirring into 500 g of a neutral wheatstarch-tragacanth thickening and adjusted with water or thickener to 1 kg of printing paste.

A mercerized cotton fabric was first printed with this paste with any design desired by means of a stencil according to the film printing process and subsequently overprinted in overlapping manner with a neutral reactive dyestuff printing paste.

This cover-print paste was prepared in the following way: 50 g of the dyestuff of the formula were dissolved by pouring 300 g of hot water on the dyestuff and the whole introduced while stirring into 500 g of a 4 percent by weight of aqueous alginate thickening, to which g'of a sequestering agent on the basis of polyphosphate and 10g of sodium of the mnitrobenzene sulfonic acid were added, before the whole was adjusted to 1 kg of printing paste with water or thickener.

After printing and drying, the cotton fabric was first developed for 5 seconds in the acid vapor in a rapid steamer System Hoechst for splitting off the diazoamino compound and for subsequent coupling by dropwise introduction of an acid mixture consisting of 5 parts of a 50 percent acetic acid and 1 part of an 85 percent formic acid, into an evaporator which is heated indirectly within the vapor chamber, the passing vapor was enriched very intensely with acid by the vaporizing acid was carrying it along.

For fixing the reactive dyestuff applied on the overprint, the fabric was then subsequently passed for 5 seconds at 95-98C through an alkaline aqueous bath containing per liter 100 g of sodium chloride 150 g of sodium carbonate g of potassium carbonate and g of a 32.5 sodium hydroxide solution and then finished as usual by washing, soaping and rins- As shown in the Example, the rapid development and fixation of the azo dyestuff according to the present process permits to fix the reactive dyestuff subsequently in a homogeneous continuous process (for example .in a wet fixing trough type Goller having a triple transport speed of a total of 6 m per 5 sec.) and to finish the good subsequently on a large-size washing machine so that, at a fixation time of 5 seconds, the whole fixation of the dyestuff and after-treatment may be carried out continuously with a transport speed of 72 m/min.

By this way, a three-colored design in blue, yellow and green was obtained, the green color being formed atthe overprinted places by exact addition of the blue of the azo dyestuff and the yellow'of the reactive dye stuff.

The same good. printing results were obtained, if a mixed fabric of polyester/cotton 67:33 was printed with the same printing pastes and, after drying of the prints and before steaming, was humidified on the reverse of the printed fabric with a thousand point roller with an acid solution consisting of l part of a 50 percent acetic acid, 1 part of an percent formic acid and 1 part of water, and subsequently steamed in a solvent steamer with ethylene glycol steam for 5 seconds at 190C.

For avoiding an excessive formation of condensate, it was suitable to pre-heat the fabric introduced into the steamer to C in a pre-posed infra-red room.

EXAMPLE 2 15 g of a commercially standardized dyeing preparation from a coupling component with the Colour Index No. 37 585 and a stabilized diazonium compound having the Colour index No. 37 were dissolved as in Example 1 and processed to a printable printing paste.

A mercerized bleached cotton fabric was printed with this paste with any design desired on a roll printing machine and subsequently provided with' overprints with a neutral reactive dyestuffiprinting paste.

This cover-print paste was prepared as in Example 1 using 30 g of the dyestuff of the formula After printing and drying the fabric, the continuous fixation of the dyestuffs and completion of the good was effected as in Example 1 by acid-steaming, subsequently alkaline wet fixation and completion on a large-size washing machine.

By this way, a three-colored design in green, orange and brown was obtained, the brown color being formed at the overprinted places byexact addition of the green of the azo dyestuff and the orange of the reactive dyestuffi EXAMPLE 3 l2 g of a commercially standardized dyeing preparation from a coupling component with the Colour Index No. 37 585 and a stabilized diazonium compound having the Colour Index No. 37 505 were dissolved as in Example 1, and a printable paste was prepared.

A mcrcerized cotton poplin was first printed with this paste with any design desired on a film printing machine and subsequently overprinted with a neutral printing paste containing a reactive'dyestuff.

This cover-print paste was prepared as in Example 1 using 50 g of the dyestuff of the formula For improving the resistance to acidic hydrolisis, 30 g of sodium acetate were added to this paste.

After printing and drying the fabric, the dyestuff was fixed by acid steaming on a perforated drum steamer of Messrs. Fleissner, Egelsbach, and subsequent wet fixation as in Example 1.

By this way a three-colored design in blue, yellow and green was obtained, the green color being formed at the overprinted places by addition of the blue of the dyestuff and the yellow of the reactive dyestuff.

As concerns the essential characteristic of the process according to the invention, the extremely rapid development and fixation of the azo dyestuffs on the fibre within a few seconds, the following Examples serve to illustrate the invention.

EXAMPLE 4 30 g of a commercially standardized dyeing preparation from a coupling component with the Colour Index No. 37 600 and a stabilized diazonium compound having the Colour Index No. 37 120 were dissolved as in Example 1 and processed to a printable printing paste. A mercerized cotton fabric was printed with the print-- ing paste thus-prepared with any design desired according to the film printing process and then dried.

For splitting off the diazoamino compound and subsequent coupling, the fabric was developed for 5 seconds in the acid vapor in a rapid steamer System Hoechst, in which process by dropwise addition of an acid mixture of 5 parts of a 50 acetic acid and 1 part of an 85 percent formic acid to an evaporator which is heated indirectly within the vapor chamber, the passing vapor was enriched very intensely with acid by the vaporizing acid carrying it along.

Then the fabric was rinsed in the boxes of a large size washing machine, soaped while boiling and rinsed again. By this way a deep brown print having a good fastness to light and an excellent fastness to wet processing was obtained with an excellentyield.

EXAMPLE 5 40 g of a commercially standardized dyeing preparation from a coupling component with the Colour Index No. 37 610 and a stabilized diazonium compound having the Colour Index No. 37 090 were dissolved as in Example 1 but without addition of urea, and processed to a printable printing paste.

After printing a spun rayon cretonne of viscosestaple fibre by means of a roller printing machine with any design desired, the fabric was dried and then nippadded before steaming on the non-printed side with an acid solution of 1 part of a 50 percent acetic acid, 1 part of an percent formic acid and 1 part of water or humidified with a thousand point roller. The subsequent steaming could be effected for 6 seconds with normal vapor, for example in a rapid steamer or preferably on a perforated drum steamer of Messrs. Fleissner, Egelsbach, so that the after-treatment could be directly carried out continuously on a large-size washing machine as in Example 1.

A yellow printing sample which was distinguished by a good fastness to light and an excellent fastness to wet processing, was obtained in an excellent yield.

EXAMPLE 6 40 g of a commercially standardized dyeing preparation from a coupling component with the Colour Index No. 37 520 and a stabilized diazonium compound having the Colour Index No. 37 090 were dissolved as in Example 1, but without addition of urea, and processed to a printable printing paste.

On a mixed fabric of polyester/cotton 67:33, any unicolored design desired was prepared with this printing paste and dried.

For developing and fixing the dyestuff, the fabric was steamed as in Example 1 on a rapid steamer System Hoechst with acid vapor for 15 seconds at 180C and finished in a fully continuous way.

A bright orange printing sample having a very good fastness to light and an excellent fastness to wet processing was obtained in a good yield and, to a large extent, a tone-in tone-dyeing of both types of fibres.

If the tonein-tone-dyeing of the different types of dyestuffs, which may vary according to the dyestuff used, will not be satisfactory enough, the color yield and the tone-in-tone-dyeing can be improved by a subsequent therrnofixation process for 30-45 seconds at I EXAMPLE 7 g of a commercially standardized dyeing preparation from the coupling component of the Colour Index No. 37590 and the Colour Index No. 37 525 and of a stabilized diazonium compound having the Colour Index No. 37 were dissolved without urea but by addition of 50 g of thiodiglycol as in Example 1, and processed to a finished printing paste with 50 g of sodium chlorate.

With this printing paste, a unicolored sample was printed on a mixed fabric of polyester/cotton 67:33 according to the roller printing process, and dried.

For developing the azo dyestuffs according to Example 5, an acid solution was applied with a thousand point roller onto the non-printed side of the fabric, which was subsequently steamed in counter-current for 15 seconds at 180C on a converscd channel steamer, wherein the channel through which the printed good was passing, was very narrow and contained additional obstacles for the steam; then the fabric was finished continuously on a large-size washing machine.

A deep black printing sample was obtained with a good yield and a satisfactory tone-in-tone-dyeing.

EXAMPLE 8 50 g of a dyeing preparation from the coupling component having the Colour Index No. 37 550 and the stabilized diazonium compound having the Colour Index No. 37 150 as well as 30 g of a disperse dyestuff of the formula OH NHZ l ll l 1 u NH2 OH were dissolved cold under addition of 20 g of a 32.5 sodium hydroxide solution 50 g of ethanol 200 g of water and 50 g of urea and dispersed, then introduced while stirring into 500 g of a neutral wheat starch-tragacanth-thickening and adjusted to 1 kg of printing paste with water or thickener.

With this printing paste any design desired was printed on a mixed fabric of polyester/cotton 67:33 according to the roller printing process. After drying the print, the reverse side of the fabric was humidified by means of a thousand point roller with an acid solution consisting of 1 part of a 50 percent acetic acid, 1 part of an 85 formic acid and 1 part of water and subsequently steamed in a solvent steamer for seconds at l90200C. For avoiding the excessive formation of condensate, the fabric introduced into the steamer was pre-heated to C in a pre-posed infra-red chamber. Fixation was carried out in the steamer with ethylene glycol vapor.

This method permits to develop and to fix, in one step, the red azo dyestuff from the dyeing preparation on the cotton portion and, at the same time, to fix the blue disperse dyestuff on the polyester portion.

We claim:

I. In a process for fixing prints of stabilized azoic dyes and reactive dyes on textile material consisting essentially of cellulose or textile materials of cellulose/- polyester mixtures by a steaming and a two-phase fixation process, the improvement which consists essentially of steaming said textile material in the presence of a vaporized carboxylic acid.

2. A process as claimed in claim 1, wherein the steaming is carried out in a steamer having a very narrow channel zone containing baffles for the acid vapor, through which channel the printed good is passed.

3. A process as claimed in claim 1, wherein said textile material has a print with an additional disperse dye which is being fixed on a polyester/cellulose mixture.

4. A process as claimed in claim 1 and wherein acid steaming is in a perforated drum zone, in which the acid-containing vapor atmosphere is passed through the textile material passing over a perforated drum zone.

5. A process as claimed in claim 11 and wherein steam is enriched with formic 'or acetic acid by means of spraying or dropping acid onto a heated evaporator near a vapor inlet pipe.

6. The process as claimed in claim 1 and wherein acid steaming is carried out in over-heated vapor of 150 200C. 1

7. The process as claimed in claim 1 and wherein acid steaming is conducted by solvent vapors instead of water steam.

8. The process as claimed in claim 7, and wherein solvent vapor is ethylene glycol vapor. 

2. A process as claimed in claim 1, wherein the steaming is carried out in a steamer having a very narrow channel zone containing baffles for the acid vapor, through which channel the printed good is passed.
 3. A process as claimed in claim 1, wherein said textile material has a print with an additional disperse dye which is being fixed on a polyester/cellulose mixture.
 4. A process as claimed in claim 1 and wherein acid steaming is in a perforated drum zone, in which the acid-containing vapor atmosphere is passed through the textile material passing over a perforated drum zone.
 5. A process as claimed in claim 1 and wherein steam is enriched with formic or acetic acid by means of spraying or dropping acid onto a heated evaporator near a vapor inlet pipe.
 6. The process as claimed in claim 1 and wherein acid steaming is carried out in over-heated vapor of 150* - 200*C.
 7. The process as claimed in claim 1 and wherein acid steaming is conducted by solvent vapors instead of water steam.
 8. The process as claimed in claim 7, and wherein solvent vapor is ethylene glycol vapor. 